1. Technical Field of the Invention
The present invention relates generally to data security, and more specifically to a technique for protecting digital content by reordering blocks of a data set.
2. Background Art
Various types of data are transmitted or otherwise transferred from one entity, such as a server, to another entity, such as a client computer or a television set-top box, via various communication paths such as broadcast, wireless, cable, modem, LAN, DSL, CD-ROM “sneakernet”, and so forth. The content of such data transmissions may be, for example, digital video, digital audio, database, graphics, spreadsheet, text, or any other form of content. The content may contain a movie, a song, a book, a television show, an electronic programming guide (EPG), an advertisement, advanced television enhancement information (ATVEF), a digital gift certificate, a digital coupon, an executable file, a data file, or any other content whatsoever. When this patent discusses examples such as a cable television company server sending an EPG to a subscriber's set-top box, the reader will understand that the invention is not necessarily limited to the specific example given, but rather that the example is given to help the reader understand the invention.
Content providers may desire to prevent corruption and/or piracy of their content, not only during transmission but also thereafter during such time as the content is stored at the receiving entity. One mechanism commonly employed to protect content is encryption, in which the digital values within the content are altered according to a cipher prior to their transmission. Many encryption schemes and methodologies are well known in the art, and will not be discussed in detail in this patent. It is assumed that the skilled reader is familiar with the relevant art.
It is also well understood that encryption of a large data set, such as a full-length movie, requires a relatively large amount of computational power and time, and that not all applications lend themselves to expense of power and/or time. This may be especially true of content which has limited economic value or which has a sufficiently short useful lifetime. The lower the value of the content, and the shorter its useful lifetime, the less justification there may be for using expensive encryption technologies to protect that content.
It is also understood that there may be many avenues of attack against content protection, with different levels of risk. Content may be attacked by different sets of actors using different sets of tools. In general, the easier and less expensive the attack, the larger the set of people who will be engaged in it. For some types of content, it may not be necessary—economically or otherwise—to protect content against all types of attack by all classes of people. For example, while the owner of a major motion picture may deem it necessary to provide strong encryption on every byte of the content at all stages of transmission and storage, the owner of an electronic programming guide covering only the next few days' broadcasts may deem it sufficient to use a weaker (and less costly) protection mechanism.
Some content, such as perhaps a nation's military secrets, may be so valuable that, in the example of a computer, it is not only desirable to protect the content which is stored on the hard drive, but further to prevent snooping attacks directed against internal wires, electromagnetic emanations from the keyboard and CRT, and so forth, on occasion even including the use of self-detonating chips which destroy themselves and their contents if someone attempts to break them open to peer inside with an electron microscope. On the other end of the spectrum, some content may be adequately protected if it is simply protected against software attacks such as those done via debuggers or memory dumps.